Process for the Preparation of an Additive-Containing Anionic Clay

ABSTRACT

Process for the preparation of an additive-containing anionic clay comprising the steps of (a) milling a physical mixture of a divalent metal compound and a trivalent metal compound, (b) calcining the physical mixture at a temperature in the range 200-800° C., and (c) rehydrating the calcined mixture in aqueous suspension, wherein an additive is present in the physical mixture and/or the aqueous suspension of step (c). With this process additive-containing anionic clays with a homogeneous additive distribution can be prepared.

The present invention relates to the preparation of anadditive-containing anionic clay.

Anionic clays have a crystal structure consisting of positively chargedlayers built up of specific combinations of divalent and trivalent metalhydroxides between which there are anions and water molecules.Hydrotalcite is an example of a naturally occurring anionic clay whereinMg is the divalent metal, Al is the trivalent metal, and carbonate isthe predominant anion present. Meixnerite is an anionic clay wherein Mgis the divalent metal, Al is the trivalent metal, and hydroxyl is thepredominant anion present.

A variety of terms is used to describe the material that is referred toin this specification as an anionic clay, such as hydrotalcite-likematerial and layered double hydroxide. In this specification we refer tothese materials as anionic clays, comprising within that termhydrotalcite-like materials and layered double hydroxides.

For several applications the presence of additives, both metals andnon-metals, within the anionic clay is desirable. These additives areused to alter or enhance certain properties of the anionic clay. Forinstance, Ce and V are added to the anionic clay to obtain materialsuitable for SO_(x) removal in FCC.

The prior art describes various methods for preparingadditive-containing anionic clays.

For instance, EP 0 278 535 describes the preparation of anadditive-containing anionic clay by co-precipitating a divalent metalsalt, a trivalent metal salt, and a rare earth metal salt out of anaqueous solution, followed by aging, filtering, washing, and drying ofthe precipitate. Unfortunately, this method generally results in aninhomogeneous distribution of the additive in the anionic clay.Furthermore, the additive may negatively affect the yield of anionicclay because, e.g., it requires a different pH range for precipitationthan the divalent and/or trivalent metal salt, or because it affects thepH of the solution in such a way as to inhibit precipitation of thedivalent and/or the divalent metal salt. In addition, this methodrequires the use of divalent and trivalent water-soluble metal salts,which are relatively expensive and which use requires (i) washing andfiltering procedures in order to remove the anions, leading to wastewater streams, and/or (ii) the emission of environmentally harmful gasesupon heating of the resulting material (e.g. NO_(x), HCl, SO_(x)).

Another way of introducing an additive into an anionic clay is by way ofimpregnation of an already prepared anionic clay, as disclosed in WO99/49001. This, however, generally leads to precipitation of theadditive as a separate phase next to the anionic clay and/or depositionof additive mainly on the outer surface of the anionic clay particles.

U.S. Pat. No. 6,028,023 discloses the preparation of an anionic clay bypreparing a mixture comprising a divalent metal-containing compound anda trivalent metal-containing compound under conditions such that aproduct obtained from the reaction mixture is a non-anionic claycompound, heat treating the non-anionic clay compound, and hydrating theheat treated non-anionic clay compound to form an anionic clay compound.The reaction mixture may contain a metallic oxidant, such as Ce, V, Pd,Pt, etc.

It has now been found that the homogeneity of the additive distributionwithin the so-obtained anionic clay can be further improved. Inaddition, smaller additive crystals can be obtained within the anionicclay. Such smaller additive crystallites provide better interaction withgaseous species during catalytic processes.

The object of the present invention is to provide a process for thepreparation of an additive-containing anionic clay which results in amore homogeneous additive distribution and/or smaller additivecrystallites than the prior art methods.

This objective is achieved by the process according to the presentinvention. This process comprises the steps of:

-   -   a) milling a physical mixture of a divalent metal compound and a        trivalent metal compound,    -   b) calcining the physical mixture at a temperature in the range        200-800° C., and    -   c) hydrating the calcined mixture in aqueous suspension to form        the additive-containing anionic clay,

wherein an additive is present in the physical mixture and/or theaqueous suspension of step c).

In this process a physical mixture of divalent and trivalent metalcompound is prepared and subsequently calcined. The term “physicalmixture” in this specification refers to a mixture of the indicatedcompounds, either in a dry or aqueous state, which compounds have notreacted with each other to any significant extent before calcinationstep b). Hence, the physical mixture has not been aged to form ananionic clay before calcination step b).

However, if the physical mixture is formed in aqueous suspension, evenwithout an aging step the formation of anionic clay cannot be fullyexcluded. In any case, formation of more than 10 wt % of anionic clay,based on the total solids content, must be prevented. Preferably, lessthan 6 wt % of anionic clay is formed, more preferably less than 2 wt %of anionic clay is formed, and most preferably no anionic clay is formedat all before the physical mixture is calcined.

In this specification the term ‘milling’ is defined as any method thatresults in reduction of the particle size. Such a particle sizereduction can at the same time result in the formation of reactivesurfaces and/or heating of the particles. Instruments that can be usedfor milling include ball mills, high-shear mixers, colloid mixers, andelectrical transducers that can introduce ultrasound waves into aslurry. Low-shear mixing, i.e. stirring that is performed essentially tokeep the ingredients in suspension, is not regarded as ‘milling’.

The physical mixture can be milled as dry powder or in suspension. Itwill be clear that, when the physical mixture is in suspension, at leastone of the metal compounds present in the mixture (so, the divalentmetal compound, the trivalent metal compound, or both) must bewater-insoluble.

Divalent Metal Compound

Suitable divalent metals include magnesium, zinc, nickel, copper, iron,cobalt, manganese, calcium, barium, strontium, and combinations thereof.The most preferred divalent metal compound is magnesium.

Suitable zinc, nickel, copper, iron, cobalt, manganese, calcium,strontium, and barium compounds are their respective water-insolubleoxides, hydroxides, carbonates, hydroxycarbonates, bicarbonates, andclays and—generally water-soluble—salts like acetates, hydroxyacetates,nitrates, and chlorides.

Suitable water-insoluble magnesium compounds include magnesium oxides orhydroxides such as MgO, Mg(OH)₂, magnesium carbonate, magnesium hydroxycarbonate, magnesium bicarbonate, hydromagnesite andmagnesium-containing clays such as dolomite, saponite, and sepiolite.Suitable water-soluble magnesium compounds are magnesium acetate,magnesium formate, magnesium(hydroxy)acetate, magnesium nitrate, andmagnesium chloride.

Preferred divalent metal compounds are oxides, hydroxides, carbonates,hydroxycarbonates, bicarbonates, and (hydroxy)acetates, as thesematerials are relatively inexpensive. Moreover, these materials do notleave undesirable anions in the additive-containing anionic clay whicheither have to be washed out or will be emitted as environmentallyharmful gases upon heating.

Trivalent Metal Compound

Suitable trivalent metals include aluminum, gallium, iron, chromium,vanadium, cobalt, manganese, nickel, indium, cerium, niobium, lanthanum,and combinations thereof. Aluminium is the most preferred trivalentmetal.

Suitable gallium, iron, chromium, vanadium, cobalt, nickel, andmanganese compounds are their respective water-insoluble oxides,hydroxides, carbonates, hydroxycarbonates, bicarbonates, alkoxides, andclays and—generally water-soluble—salts like acetates, hydroxyacetates,nitrates, and chlorides. Suitable water-insoluble aluminium compoundsinclude aluminium oxides and hydroxides such as transition alumina,aluminium trihydrate (Bauxite Ore Concentrate, gibbsite, bayerite) andits thermally treated forms (including flash-calcined aluminiumtrihydrate), sols, amorphous alumina, and (pseudo)boehmite,aluminium-containing clays such as kaolin, sepiolite, bentonite, andmodified clays such as metakaolin. Suitable water-soluble aluminiumsalts are aluminium nitrate, aluminium chloride, aluminiumchlorohydrate, and sodium aluminate.

Preferred trivalent metal compounds are oxides, hydroxides, carbonates,bicarbonates, hydroxycarbonates, and (hydroxy)acetates, as thesematerials are relatively inexpensive. Moreover, these materials do notleave undesirable anions in the additive-containing anionic clay whicheither have to be washed out or will be emitted as environmentallyharmful gases upon heating.

Step A)

The first step in the process of the invention involves milling of aphysical mixture of the divalent and the trivalent metal compound.

This physical mixture can be prepared in various ways. The divalent andtrivalent metal compound can be mixed as dry powders or in (aqueous)suspension thereby forming a slurry, a sol, or a gel. In the lattercase, the divalent and trivalent metal compound are added to thesuspension as powders, sols, or gels and the preparation and milling ofthe mixture is followed by drying.

If the physical mixture is prepared in aqueous suspension, dispersingagents can be added to the suspension. Suitable dispersing agentsinclude surfactants, phosphates, sugars, starches, polymers, gellingagents, swellable clays, etc. Acids or bases may also be added to thesuspension.

The molar ratio of divalent to trivalent metal in the physical mixturepreferably ranges from 0.01 to 10, more preferably 0.1 to 5, and mostpreferably 1 to 3.

The physical mixture is milled, either as dry powder or in suspension.In addition to milling of the physical mixture, the divalent metalcompound and the trivalent metal compound may be milled individuallybefore forming the physical mixture.

When the physical mixture is milled in suspension, the mixture is wetmilled during about 1-30 minutes at room temperature, for instance in aball mill, a bead mill, a sand mill, a colloid mill, a high shear mixer,a kneader, or by using ultrasound. After wet milling and beforecalcination, the physical mixture must be dried.

The preferred average size of the particles obtained after milling isabout 0.1 to 10 microns, more preferably about 0.5 to 5 microns, mostabout 1-3 microns.

The temperature during milling may be ambient or higher. Highertemperatures may for instance result naturally from the milling processor may be generated by external heating sources. Preferably, thetemperature during milling ranges from 20 to 90° C., more preferablyfrom 30 to 50° C.

Step B)

The physical mixture is calcined at a temperature in the range of200-800° C., more preferably 300-700° C., and most preferably 350-600°C. Calcination is conducted for 0.25-25 hours, preferably 1-8 hours, andmost preferably 2-6 hours. All commercial types of calciners can beused, such as fixed bed or rotating calciners.

Calcination can be performed in various atmospheres, e.g., in air,oxygen, inert atmosphere (e.g. N₂), steam, or mixtures thereof.

The so-obtained calcined material must contain hydratable oxide. Theamount of hydratable oxide formed depends on the type of divalent andtrivalent metal compound used and the calcination temperature.Preferably, the calcined material contains 10-100% of hydratable oxide,more preferably 30-100%, even more preferably 50-100%, and mostpreferably 70-100% of hydratable oxide. The amount of hydratable oxideformed in step b) is equivalent to and calculated from the amount ofanionic clay obtained in step c). This amount can be determined bymixing various known amounts of pure anionic clay with samples of thehydrated product of step c). Extrapolation of the relative intensitiesof anionic clay to non-anionic clay in these mixed samples—as measuredwith Powder X-Ray Diffraction (PXRD)—can then be used to determine theamount of anionic clay in the hydrated product. An example of an oxidethat is not hydratable is a spinel-type oxide.

Step C)

Hydration of the calcined material is conducted by contacting thecalcined mixture with a water or an aqueous solution of anions. This canbe done by passing the calcined mixture over a filter bed withsufficient liquid spray, or by suspending the calcined mixture in theliquid. The temperature of the liquid during hydration is preferablybetween 25 and 350° C., more preferably between 25 and 200° C., mostpreferably between 50 and 150° C., the temperature of choice dependingon the nature of the divalent and trivalent metal compound used.Hydration is performed for about 20 minutes to 20 hours, preferably 30minutes to 8 hours, more preferably 1-4 hours.

During hydration, the suspension can be milled by using high-shearmixers, colloid mixers, ball mills, kneaders, ultrasound, etc.

Hydration can be performed batch-wise or continuously, optionally in acontinuous multi-step operation according to pre-published U.S. patentapplication no. 2003-0003035. For example, the hydration suspension isprepared in a feed preparation vessel, whereafter the suspension iscontinuously pumped through two or more conversion vessels. Additives,acids, or bases, if so desired, can be added to the suspension in any ofthe conversion vessels. Each of the vessels can be adjusted to its owndesirable temperature.

During hydration, anions can be added to the liquid. Examples ofsuitable anions include inorganic anions like NO₃ ⁻, NO₂ ⁻, CO₃ ²⁻, HCO₃⁻, SO₄ ²⁻, SO₃NH₂, SCN⁻, S₂O₆ ²⁻, SeO₄ ⁻, F⁻, Cl⁻, Br⁻, I⁻, ClO₃ ⁻, ClO₄⁻, BrO₃ ⁻, and IO₃ ⁻, silicate, aluminate, and metasilicate, organicanions like acetate, oxalate, formate, long chain carboxylates (e.g.sebacate, caprate and caprylate (CPL)), alkylsufates (e.g.dodecylsulfate (DS) and dodecylbenzenesulfate), stearate, benzoate,phthalocyanine tetrasulfonate, and polymeric anions such as polystyrenesulfonate, polyimides, vinylbenzoates, and vinyidiacrylates, andpH-dependent boron-containing anions, bismuth-containing anions,thallium-containing anions, phosphorus-containing anions,silicon-containing anions, chromium-containing anions,vanadium-containing anions, tungsten-containing anions,molybdenum-containing anions, iron-containing anions, niobium-containinganions, tantalum-containing anions, manganese-containing anions,aluminium-containing anions, and gallium-containing anions.

The Additive

The additive to be used in the process according to the presentinvention is a compound comprising an element selected from the group ofalkaline earth metals (for instance Mg, Ca and Ba), Group IIIAtransition metals, group IVA transition metals (e.g. Ti, Zr), Group VAtransition metals (e.g. V, Nb), Group VIA transition metals (e.g. Cr,Mo, W), Group VIIA transition metals (e.g. Mn), Group VIIIA transitionmetals (e.g. Fe, Co, Ni, Ru, Rh, Pd, Pt), Group IB transition metals(e.g. Cu), Group IIB transition metals (e.g. Zn), Group IIIB elements(e.g. B, Al, Ga), Group IVB elements (e.g. Si, Sn), Group VB elements(e.g. P), lanthanides (e.g. La, Ce), and mixtures thereof, provided thatthe element differs from the metals constituting the divalent and thetrivalent metal compound of step a).

Preferred elements are La, Ce, V, Mo, W, P, Pt, Pd, and Nb.

The additive is preferably an oxide, hydroxide, carbonate, orhydroxycarbonate of the desired element.

One or more additive(s) is/are present in the physical mixture and/or tothe aqueous suspension of step c). Preferably, an additive is alreadypresent in the physical mixture.

If present in the physical mixture, the additive can be added to thephysical mixture before or during milling step a), during calcinationstep b), or between milling step a) and calcination step b). Additionduring calcination requires the use of a calciner with sufficient mixingcapability that can be effectively used as mixer as well as calciner.

The additive can be added to the physical mixture in step a) and thesuspension of step c) as a solid powder, in suspension or, preferably,in solution. If added during calcination, it is added in the form of apowder.

Additional Calcination and Hydration Steps

The resulting additive-containing anionic clay can be subjected to anadditional calcination and optionally an additional hydration step.

The so-formed calcined material can be used as a catalyst or sorbent forvarious purposes, such as FCC processes. If this calcination is followedby a subsequent hydration, an additive-containing anionic clay is formedanalogous to the one formed after the first hydration step, but with anincreased mechanical strength.

These second calcinations and hydration steps may be conducted underconditions which are either the same or different from the firstcalcination and hydration steps.

Additional additives may be added during this additional calcinationstep and/or during this hydration step. The additives disclosed underthe heading ‘additive’ above may all be suitably used for this purpose.These additional additives can be the same or different from theadditive present in the physical mixture and/or the aqueous suspensionof step c).

Furthermore, during this additional hydration step, anions can be added.Suitable anions are the ones mentioned above in relation to the firsthydration step. The anions added during the first and the additionalhydration step can be the same or different.

Compositions Comprising the Additive-Containing Anionic Clay

If so desired, the additive-containing anionic clay prepared accordingto the process of the present invention can be mixed with conventionalcatalyst or sorbent ingredients such as silica, alumina,aluminosilicates, zirconia, titania, boria, (modified) clays such askaolin, acid leached kaolin, dealuminated kaolin, smectites, andbentonite, (modified or doped) aluminium phosphates, zeolites (e.g.zeolite X, Y, REY, USY, RE-USY, or ZSM-5, zeolite beta, silicalites),phosphates (e.g. meta or pyro phosphates), pore regulating agents (e.g.sugars, surfactants, polymers), binders, fillers, and combinationsthereof.

The additive-containing anionic clay, optionally mixed with one or moreof the above conventional catalyst components, can be shaped to formshaped bodies. Suitable shaping methods include spray-drying,pelletising, extrusion (optionally combined with kneading), beading, orany other conventional shaping method used in the catalyst and absorbentfields or combinations thereof.

Use of the Additive-Containing Anionic Clay

The additive-containing anionic clay prepared by the process accordingto the invention is very suitable for use as sulfur oxide sorbentmaterial. Hence, the material can be incorporated for this purpose inFCC catalysts or FCC catalyst additives. Additionally, theadditive-containing anionic clay can be used for the adsorption ofsulfur oxide emission from other sources, like power plants.

As sulfur oxides sorbent materials are generally good nitrogen oxidesorbent materials, the additive-containing anionic clay will likewise besuitable as nitrogen oxide sorbent material in, e.g., FCC catalysts, FCCcatalyst additives, etc.

Furthermore, it can be used for other purposes, such as the removal ofgases like HCN, ammonia, Cl₂, and HCl from steel mills, power plants,and cement plants, for reduction of the sulphur and/or nitrogen contentin fuels like gasoline and diesel, as additives for the conversion of COto CO₂, and in or as catalyst compositions for Fischer-Tropschsynthesis, hydroprocessing (hydrodesulfurisation, hydrodenitrogenation,demetallisation), hydrocracking, hydrogenation, dehydrogenation,alkylation, isomerisation, Friedel Crafts processes, ammonia synthesis,etc.

If so desired, the additive-containing anionic clay can be treated withorganic agents, thereby making the surface of the clay—which isgenerally hydrophilic in nature—more hydrophobic. This allows for theadditive-containing anionic clay to disperse more easily in organicmedia.

When applied as nanocomposites (i.e. particles with a diameter less thenabout 500 nm), the additive-containing anionic clay can suitably be usedin plastics, resins, rubber, and polymers. Nanocomposites with ahydrophobic surface, for instance obtained by treatment with an organicagent, are especially suited for this purpose.

EXAMPLES Comparative Example 1

An aqueous physical mixture comprising 41.28 g Gibbsite (the trivalentmetal compound), and 64.03 g MgO (the divalent metal compound) wasprepared in 185 g distilled water. To the resulting slurry, a ceriumnitrate solution comprised of 27.56 g cerium nitrate (the additive)dissolved in 27.1 g of distilled water was added. The pH of theresulting slurry was adjusted to 9 with ammonium hydroxide.

After the pH adjustment, the slurry was immediately dried in aconvection oven at 110° C. The dried powder was calcined at 500° C. forfour hours. PXRD did not show anionic clay formation before calcination.

A 20.0 g portion of the resulting calcined powder was hydrated in anammonium metavanadate solution comprising 1.29 g of ammoniummetavanadate (an additive) in 175 g distilled water. Hydration wasconducted at 85° C. overnight. The slurry was then filtered, washed withdistilled water and dried at 110° C.

The amount of hydratable oxide (measured as described in thespecification above) present after calcination was 80%.

Example 2

Comparative Example 1 was repeated, except that after the pH adjustment,the slurry was high shear mixed in a Waring blender for 20 minutesbefore being dried at 110° C.

Also here, PXRD did not show anionic clay formation before calcination.The amount of hydratable oxide present after calcination was 80%.

Comparative Example 3

Comparative Example 1 was repeated, except that the 20.0 g portion ofthe calcined powder was hydrated in 650 g of a 1M sodium carbonatesolution overnight at 85° C.

The amount of hydratable oxide present after calcination was 70%.

Example 4

Comparative Example 3 was repeated, except that after the pH adjustment,the slurry was high shear mixed in a Waring blender for 20 minutesbefore being dried at 110° C.

Also here, PXRD did not show anionic clay formation before calcination.

The amount of hydratable oxide present after calcination was 70%.

Comparative Example 5

An aqueous physical mixture was prepared by dispersing 35.17 g Gibbsite,48.84 g calcium carbonate, and 27.27 g MgO in 115 g distilled water. Tothe resulting slurry, a cerium nitrate solution comprising 26.71 gcerium nitrate dissolved in 26.2 g of distilled water was added. The pHof the resulting slurry was adjusted to 9 with ammonium hydroxide. Theslurry was immediately dried in a convection oven at 110° C. The driedpowder was calcined at 500° C. for four hours.

PXRD did not show anionic clay formation before calcination.

A 20.0 g portion of the resulting calcined powder was hydrated in anammonium metavanadate solution comprised by dissolving 1.29 g ofammonium metavanadate in 175 g distilled water overnight at 85° C. Theslurry was then filtered, washed with distilled water and dried at 110°C.

The amount of hydratable oxide present after calcination was 10%.

Example 6

Comparative Example 5 was repeated, except that after the pH adjustment,the slurry was high shear mixed in a Waring blender for 20 minutesbefore being dried at 110° C.

PXRD did not show anionic clay formation before calcination.

The amount of hydratable oxide present after calcination was 10%.

Example 7

Example 2 was repeated, except that a 15.0 g portion of the calcinedpowder was hydrated in a ammonium metavanadate solution comprised bydissolving 2.89 g of ammonium metavanadate in 136 g distilled waterovernight at 85° C.

The amount of anionic clay in the hydrated product (as determined by themethod indicated in the specification above) was 80%.

Example 8

Powder X-ray diffraction (PXRD) patterns of the samples of Examples 1-6indicated as reflection at 28.5° 2-theta, indicating the presence ofCeO₂ (See ICDD file 81-0792, using CuK_(a) radiation.

The full width at half maximum (FWHM) of this reflection in thedifferent samples was determined. See Table 2. TABLE 2 Example FWHM (°2-theta) 1 (comp.) 2.03 2 2.76 3 (comp.) 2.03 4 2.16 5 (comp.) 3.1  6too broad to be measured

It is generally known that the crystallite size is inversely related tothe FWHM of an individual peak. The broader the peak, the smaller thecrystallite size. So, the above results show that milling of thephysical mixture results in the formation of smaller additivecrystallites, indicating a more homogeneous additive distribution.

Example 9

The products of Examples 2, 4, 6, and 7 were tested for their de-SO_(x)ability in FCC processes using the thermographimetric test described inInd. Eng. Chem. Res. Vol. 27 (1988) pp. 1356-1360. A standard commercialde-SO_(x) additive was used as a reference.

Known weights of the samples and the same weight of the standardcommercial additive were heated under nitrogen at 700° C. for 30minutes. Next, the nitrogen was replaced by a gas containing 0.32% SO₂,2.0% O₂, and balance N₂ with a flow rate of 200 mllmin. After 30 minutesthe SO₂-containing gas was replaced by nitrogen and the temperature wasreduced to 650° C. After 15 minutes, nitrogen was replaced by pure H₂and this condition was maintained for 20 minutes. This cycle wasrepeated 3 times. The sample's SO_(x) uptake and its release duringhydrogen treatment were measured as the sample's weight change (in %).

The ratio of SO_(x) release over SO_(x) uptake was defined as theeffectiveness ratio The ideal effectiveness ratio is 1, which means thatall the SO_(x) that was taken up was released again, leading to a longercatalyst life.

Table. 2 indicates the effectiveness ratio of the samples preparedrelative to the effectiveness ratio of the commercial de-SO_(x)additive: the SO_(x) improvement.

A SO_(x) improvement of 1 means that the prepared sample has the sameeffectiveness ratio as the commercial additive. An improvement higherthan 1 indicated that a higher effectiveness ratio was obtained. TABLE 2Example SO_(x) improvement 2 0.98 4 0.97 6 1.85 7 0.98

This table shows that the effectiveness ratio of the compositionsprepared according to the invention is comparable to and, in case ofExample 6, significantly higher than that of a commercial additive. Inother words, the compositions prepared according to the invention arevery suitable as additives in FCC process for the reduction of SO_(x)emissions.

1. A process for the preparation of an additive-containing anionic claycomprising the steps of: a) milling a physical mixture of a divalentmetal compound and a trivalent metal compound, b) calcining the milledphysical mixture at a temperature in the range 200-800° C., and c)rehydrating the calcined mixture in aqueous suspension to form theadditive-containing anionic clay, wherein an additive is present in thephysical mixture and/or the aqueous suspension of step (c).
 2. Theprocess according to claim 1 wherein the milling is performed in a ballmill, a bead mill, a sand mill, a colloid mill, a kneader, or a highshear mixer, or by using ultrasound.
 3. The process according to claim 1wherein the calcination temperature ranges from 300 to 700° C.
 4. Theprocess according to claim 3 wherein the calcination temperature rangesfrom 350 to 600° C.
 5. The process according to claim 1 wherein thedivalent metal is selected from the group consisting of Mg, Zn, Ni, Fe,Co, Ca, Sr, Ba, Mn, Cu and combinations thereof.
 6. The processaccording to claim 1 wherein the trivalent metal is selected from thegroup consisting of Al, Ga, Fe, Cr, V, Mn, Co, Ni and combinationsthereof.
 7. The process according to claim 1 wherein the additive isselected from the group consisting of La, Ce, V, Mo, W, P, Pt, Pd, Nb,and combinations thereof.
 8. The process according to claim 1 followedby calcination of the formed additive-containing anionic clay.
 9. Theprocess according to claim 8 followed by rehydration of the calcinedadditive-containing anionic clay.